Professional Fitting And Information Guide For Trade Name (generic name) Rigid Gas Permeable Contact Lenses For Orthokeratology
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TABLE OF CONTENTS
Introduction
Product Description
Lens Parameters Available
Actions
Indications
Contraindications, Warnings, and Adverse Reactions
Precautions
Selection of Patients
Fitting Procedure
Orthokeratology Lens Description
Predicting Lens Results
Clinical Study Results
Myopic Reduction Maintenance Lens or Retainer Lens Wear
Risk Analysis
Fitting TN Contact Lenses for Orthokeratology
Pre-fitting Examination
Initial Lens Power Selection
Initial Lens Diameter Selection
Initial Lens Base Curve Selection
Initial Lens Evaluation
Trial Lenses
Follow-Up Care
Ortho-K Problem Solving
Recommended Initial Wearing Schedule
Handling of Lenses
Patient Lens Care Directions
Vertex Distance and Keratometry Conversion Charts
Reporting of Adverse Reactions
How Supplied
Package Insert
Trade Name contact lenses for orthokeratology are made from a [fluoro silicone acrylate] [silicone acrylate] [etc.] polymer with a water content of # percent. The lenses are to be worn for [daily wear only.][overnight wear from one to # days between cleaning and disinfection as recommended by the eye care practitioner.]
The TN contact lens for orthokeratology is a rigid gas permeable contact lens in a reverse geometry design. The lens material, [generic name], is a [fluoro silicone acrylate] [silicone acrylate] [etc.] polymer which contains [listed color additive] as a color additive. The TN contact lens for orthokeratology has the following dimensions:
Chord Diameter
Center Thickness
for Low Minus Lens:
for Plus Lens:
Base Curve
Secondary Curves
Flatter or Steeper than Base Curve
Peripheral Curves
Flatter or Steeper than Base Curve
Powers
Aspheric Lens Eccentricity
(Oblate, Prolate or Tangent Conic)
The physical properties of the lens are:
Refractive Index
Light Transmittance
Wetting Angle
(Contact Receding Angle)
Specific Gravity
Hardness
Water Content
Oxygen Permeability and method
TN contact lenses for orthokeratology produce a temporary reduction of myopia by changing the shape (flattening) of the cornea, which is elastic in nature. Flattening the cornea reduces the focusing power of the eye, and if the amount of corneal flattening is properly controlled, it is possible to bring the eye into correct focus and compensate for myopia. Contact lenses rest directly on the corneal tear layer and can influence the corneal shape. Regular contact lenses are designed to cause little or no effect but TN contact lenses for orthokeratology are designed to purposely flatten the shape of the cornea by applying slight pressure to the center of the cornea. If the cornea is flattened this reduces the focusing power of the eye, and if the amount of corneal flattening is sufficient, it is possible to bring the eye into correct focus and compensate for myopia. After the contact lens is removed, the cornea retains its altered shape for part or all of the remainder of the day. A myopic reduction maintenance lens or retainer lens must be worn each day to maintain the corneal flattening, or the myopia will revert back to the pre-treatment level.
The TN (generic name) Rigid Gas Permeable Contact Lenses for orthokeratology are indicated for use in the reduction of myopic refractive error in non-diseased eyes. The lens is indicated for [daily wear] [extended wear from 1 to # days between removals for cleaning and disinfection as recommended by the eye care practitioner] in an orthokeratology fitting program for the temporary reduction of myopia of up to # diopters. The lenses may be disinfected using a chemical disinfection system only.
Note: To maintain the orthokeratology effect of myopia reduction lens wear must be continued on a prescribed wearing schedule.
CONTRAINDICATIONS (REASONS NOT TO USE) WARNINGS AND ADVERSE REACTIONS:
DO NOT USE TN contact lenses for orthokeratology when any of the following conditions exist:
- Acute and subacute inflammations or infection of the anterior segment of the eye.
- Any eye disease, injury, or abnormality that affects the cornea, conjunctiva or eyelids.
- Severe insufficiency of tears (dry eyes)
- Corneal hypoesthesia (reduced corneal sensitivity).
- Any systemic disease which may affect the eye or be exacerbated by wearing contact lenses.
- Allergic reactions of ocular surfaces or adnexa which may be induced or exaggerated by wearing contact lenses or use of contact lens solutions.
- Allergy to any ingredient, such as mercury or Thimerosal, in a solution which is to be used to care for contact lenses.
- Any active corneal infection (bacterial, fungal or viral).
- If eyes become red or irritated.
Caution: TN contact lenses for orthokeratology are shipped to the practitioner non-sterile. Clean and condition lenses prior to use.
Clinical studies have demonstrated that contact lenses manufactured from the TN contact lens for orthokeratology materials are safe and effective for their intended use. However, due to the small number of patients enrolled in clinical investigation of lenses, all refractive powers, design configurations, or lens parameters available in the lens material were not evaluated in significant numbers. Consequently, when selecting an appropriate lens design and parameters, the eye care practitioner should consider all characteristics of the lens that can affect lens performance and ocular health, including oxygen permeability, wettability, central and peripheral thickness, and optic zone diameter.
The potential impact of these factors on the patient's ocular health should be carefully weighed against the patient's need for refractive reduction; therefore, the continuing ocular health of the patient and lens performance on the eye should be carefully monitored by the prescribing eye care practitioner.
Patients are selected who have a demonstrated need and desire for a refractive reduction by orthokeratology with rigid gas permeable contact lenses and who do not have any of the contraindications for contact lenses described above. TN contact lenses for orthokeratology are indicated for myopic patients who desire to have time periods during the day, in which they do not need to wear their contact lenses, but still be able to see clearly. This might include such activities as swimming and other sports. TN contact lenses for orthokeratology may be useful in occupations that require exposure to smoke, noxious gases or conditions of low humidity, such as would be the case for flight attendants, if their lenses can be worn before exposure to the noxious substance and removed during its presence. Some patients are content to wear their contact lenses for normal activities during part of the day and remove them for evening activities.
TN contact lenses for orthokeratology are primarily intended for patients who are within the following parameters.
| Refractive error: | # to # diopters |
| Keratometry | # to # diopters; |
| Visual Acuity | 20/# to 20/# |
TN contact lenses for orthokeratology are designed to be fitted so as to flatten the central cornea and thereby reduce myopia. This goal is accomplished by the lens design and the manner in which the lens is fitted.
The TN contact lens for orthokeratology has a design known as reverse geometry. This means that the secondary curve on the posterior surface has a radius of curvature that is steeper (shorter radius) than the base curve (central curve). The secondary curve is surrounded by a flatter peripheral curve near the edge [(Figure 1)]. In this way the geometry of the secondary curve is in the opposite relationship to the base curve, as occurs with standard rigid gas permeable contact lenses.
The function of the steep secondary curve in the TN contact lens for orthokeratology is to allow the base curve to be fitted flat in relation to the central cornea and still maintain lens stability on the cornea. With a regular contact lens design, that is fitted flat on the cornea, there is only one support point for the contact lens, which occurs at the center of the lens. This lens will tend to rock and decenter on the cornea. With the TN contact lens for orthokeratology there is support for the lens at both the central cornea and also in the area of the secondary curve. This will tend to reduce lens rocking and aid in centering.
The most commonly used lens design for the TN contact lens for orthokeratology has a secondary curve that is [#]diopters, steeper (higher power) than the base curve. The peripheral curve is a standard flatter curve. The secondary curve relationship can be altered to achieve an optimal lens design for each patient. Normally the secondary curve is between # and # diopters steeper than the base curve. In some lenses the secondary curve is divided into two curves of nearly equal width. The inner portion of the secondary curve is equivalent to the usual radius value of the TN lens and the outer portion is flattened to provide a smooth transition to the peripheral curve, in the manner of a blend.
Various methods have been proposed for predicting the amount of corneal flattening that may be achieved for a given patient by orthokeratology. There is some evidence that patients with corneas of higher eccentricities are more likely to undergo greater amounts of corneal flattening than do patients with more spherical corneas. Corneal eccentricity can be measured by video keratography or by comparing central and peripheral keratometry readings. Other studies have not supported these conclusions, however, and further research is needed. It is not possible at this time to predict which patients will achieve the greatest corneal flattening with TN contact lenses for orthokeratology.
TN contact lenses for orthokeratology may produce a temporary reduction of all or part of a patient's myopia. The amount of reduction will depend on many factors including the amount of myopia, the elastic characteristics of the eye and the way that the contact lenses are fitted. Average amounts of reduction have been established by clinical studies but the reduction for an individual patient may vary significantly from the averages.
A total of # (# patients) eyes were enrolled in the clinical study with # eyes (# patients) completing a minimum of [three] [twelve] months of contact lens wear. Of the completed eyes a total of # eyes showed some reduction in myopic refractive error during the [3][12]-month time period that the TN contact lenses for orthokeratology were worn. This included:
- # eyes (#%) had a reduction of between 0.25 and 1.00 D,
- # eyes (#%) between 1.25 and 2.00 D,
- # eyes (#%) between 2.25 and 3.00 D,
- # eyes (#%) between 3.25 and 4.00 D and,
- # eye (# %) reduced by 4.25 D
Other clinical refractive outcomes:
- # eyes had no change and # eyes increased in minus power by 0.25D.
- The reduction in myopia was [greater][less] for eyes with a higher initial refractive error.
- # eyes over -3.50D were able to achieve a full reduction in myopia.
- For # eyes with an initial myopia of greater than 3.75D the average final exam reduction in myopia was [#D].
- The limit in initial myopia that could be reduced to emmetropia in was [#D].
The average amount of myopia that can be expected to be corrected is shown in the following table. These values are only averages and some patients can be expected to achieve more or less than these averages.
AVERAGE REDUCTION IN MYOPIA (Diopters)
|
INITIAL |
REDUCTION |
| -1.00 | # |
| -2.00 | # |
| -3.00 | # |
| -4.00 | # |
| Etc. | # |
The average reduction was # diopters with a range from # to # diopters. The amount of myopia reduced varied between patients and could not be predicted prior to treatment. There [was] [was not] an insignificant difference between the patients who wore contact lenses prior to the study and those with no previous contact lens experience.
TN contact lenses for orthokeratology provided a temporary full reduction in some patients with up to # diopters of myopia. For patients with greater than # diopters of myopia only a partial reduction of myopia can be expected. The percentage of patients that can be expected to achieve full or partial temporary refractive reduction is shown in the following table:
PERCENT OF EYES THAT ACHIEVED FULL OR PARTIAL
TEMPORARY REDUCTION OF MYOPIA
|
INITIAL |
FULL |
UP TO 0.50 D. |
FINAL V.A. |
FINAL V.A. |
|
1.00> |
% | % | % | % |
| -1.25 to - 2.00 D. |
% | % | % | % |
| -2.25 to - 3.00 D. |
% | % | % | % |
| -3.25 to - 4.00 D. |
% | % | % | % |
| Etc. | % | % | % | % |
For the patients (# eyes) that completed the study, the initial visual acuity by best refraction was 20/20 or better for # eyes and 20/40 or better for # eyes. At the final visit, visual acuity with contact lenses was equal to or better than 20/20 for # eyes, 20/40 for # eyes and # eyes had a visual acuity of 20/[#]. # eyes had a one-line drop in visual acuity for contact lenses compared to best refraction, # eyes had a two-line drop and # eyes had a three-line drop.
The percentage of eyes that achieved uncorrected visual acuity of 20/20 or better and 20/40 or better in relation to the initial myopia is given in the above table. A total of # (#%) eyes achieved a visual acuity of 20/20 or better and # (# %) eyes achieved 20/40 or better.
EFFECTS ON ASTIGMATISM
Either increases or decreases in astigmatism may occur following orthokeratology. Of the # eyes (# patients) which completed the [three][twelve] month clinical study, #% showed no change in corneal astigmatism, #% showed a decrease less than one diopter, while # % showed an increase less than one diopter and #% showed an increase greater than one diopter.
The following changes were noted:
| Decrease | |||
| . | from 0.12 to l.00 D was observed for #eyes (#%) | ||
| . | from l.12 to l.50 D for #eyes (#%) | ||
| . | more than 1.50 D for # eyes (#%) | ||
| Increase | |||
| . | from 0. 1 2 to 1.00 D was observed for # eyes (# %) from 1. 1 2 to 2.00 D for # eyes (#%) |
||
| . | from 2.12 to 3.00 D for # eyes (# %) | ||
| . | from 3.12 to 3.50 D for # eyes (# %) more than 3.50D for # eyes (#%) |
WEARING TIME
The average wearing time required for patients who wore TN contact lenses for orthokeratology for various time periods was as follows:
| One week | hours/days |
| Two weeks | hours/days |
| One month | hours/days |
| Three months | hours/days |
| Etc. | hours/days |
There was considerable variability, however, as many patients required several [hours][days] more or less than the averages as shown for the [three][twelve]-month time period as follows:
| Daily Wear | |||
| Time Worn | Percent of patients | ||
| 0 to 4 hours | #% | 4.1 to 8 hours | #% |
| 8.1 to 12 hours | #% | 12.1 to 16 hours | #% |
Overnight Wear |
|||
| 1 to 3 days | |||
| Ec. |
MYOPIC REDUCTION MAINTENANCE LENS OR RETAINER LENS WEAR
Studies have shown that the long-term wear of TN contact lenses for orthokeratology does not eliminate the need to continue wearing contact lenses in order to maintain the orthokeratology effect. After the cornea has been flattened by wearing TN contact lenses for orthokeratology, the patient will need to continue wearing Myopic Reduction Maintenance Lenses or Retainer lenses for a portion of each day. A Retainer lens may be either the last TN contact lens for orthokeratology design or a modification of this design in which the central portion of the lens applies just enough pressure to the cornea to maintain the corneal flattening achieved but with no additional corneal flattening. The last pair of lenses in the fitting program is usually used as the first Retainer Lens. If it is found that this lens has a secondary curve that is too tight for the lens to be worn on a long-term basis, a new Retainer Lens is prescribed which has the same base curve but a flatter secondary curve, usually by one or two diopters. The retainer lenses are generally worn for the same daily schedule as the TN contact lenses for orthokeratology and must be worn each day to maintain the orthokeratology effect.
One of the most common and effective schedules is to wear the retainer lens for several hours in the morning and a few hours before bedtime. Higher lens powers may require additional wearing time.
It is important to make certain that the retainer lenses center well on the cornea, as the same lens will be worn for a prolonged period. Check the patient's lenses every 3 to 4 months.
There is a small risk involved when any contact lens is worn. It is not expected that the TN contact lens for orthokeratology will provide a risk that is greater than other rigid gas permeable contact lenses.
The two most common side effects that occur in rigid contact lens wearers are corneal edema and corneal staining. It is anticipated that the same side effects will also occur in some wearers of TN contact lenses for orthokeratology. Other side effects that sometimes occur in all contact lens wearers are pain, redness, tearing, irritation, discharge, abrasion of the eye or distortion of vision. These are usually temporary conditions if the contact lenses are removed promptly.
In rare instances, there may occur permanent corneal scarring, decreased vision, infections of the eye, corneal ulcer, iritis, or neovascularization. The occurrence of these side effects should be minimized or completely eliminated if proper patient control is exercised. Patients should be instructed to remove the contact lenses if any abnormal signs are present. Patients should be instructed never to wear their contact lenses while in the presence of noxious substances. Patients should be instructed in the importance and necessity of returning for all follow-up visits required by the eye care practitioner.
[Studies have not been conducted to support the safety and effectiveness of wearing TN contact lenses for orthokeratology for overnight wear.]
TN contact lenses for orthokeratology may be fitted using a modification of the standard techniques for rigid gas permeable contact lenses.
| 1. | Prefitting Examination: | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| A. | complete refraction and visual health examination should be performed. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
| B. | pre-fitting patient history and examination are necessary to:
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| 2. |
Standard procedures for determining power of rigid gas permeable contact lenses may be used, including compensation for vertex distance. |
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3. |
Usually, lens diameters between # mm to # mm are chosen to maximize centering to the cornea and to minimize lens movement. Lens diameters outside of this range are occasionally used for some eyes. This guide is only a general recommendation and the specification for an individual patient will depend on the eye care practitioner's professional judgment.
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4. |
The base curve of the first lens fitted is generally fitted about # diopters flatter than the flattest keratometric finding but may vary according to the following table, which takes into account the corneal astigmatism. This guide is only a general recommendation and the specification for an individual patient will depend on the eye care practitioner's professional judgment.
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5. |
Initial Lens Evaluation
Trial Lens Fitting Trial lens fitting is recommended whenever possible. Trial lens fitting allows a more accurate determination of lens specifications for the lens fit and power. Choose the first lens according to the table given for base curve selection. Trial lenses are essential in fitting patients whose corneal topography has been distorted by previous contact lens wear. Trial Lens Set A basic trial lens set consists of [describe lenses in this set]. CAUTION: Non-sterile lenses, clean and condition lenses prior to use. Eye care practitioners should educate contact lens technicians concerning proper care of trial lenses. Each contact lens is shipped non-sterile in a case with no solution (dry). Therefore in order to insure disinfection, clean and condition lenses prior to use. Hands should be thoroughly washed and rinsed and dried with a lint free towel prior to handling a lens. Prior to reusing in a diagnostic procedure or before dispensing to a patient, lenses should be surface cleaned and disinfected, following the manufacturer's instruction. Trial Lens Procedure Select a trial lens and place the lens upon the eye. Evaluate the lens using white light for the following:
Limits of Flattening In some cases the corneal flattening stops before a full reduction of the refractive error has been accomplished. Additional flattening may be possible by using a lens with a steeper secondary curve (# or # diopters steeper than the base curve). If no further corneal flattening occurs, it is an indication that the patient should be fitted with a retainer lens.
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